1. Field of the Invention
This invention relates to scaffold planks in general and more particularly to a combination scaffold plank designed to incorporate the safety features of wooden scaffold planks and the safety and economic features of metal scaffold planks while eliminating the disadvantages associated with both of these types of scaffold planks.
2. Description of the Prior Art
Scaffolding is used in a wide range of industrial/construction settings. Generally speaking, scaffolding is comprised of two primary components. The first component is a metal frame that is erected alongside or about a structure upon which work is to be performed. The second component is scaffold planks. Scaffold planks rest upon the metal frame, or are lapped upon other scaffold planks which in turn rest upon the metal frame, and provide the platform upon which workers and equipment can be placed.
The most common scaffold plank utilized in the scaffold industry is a wooden plank. The wood used in wooden planks has a good coefficient of friction, thereby reducing the risk of the wooden plank slipping off of the metal frame, or the scaffold plank it is resting upon, when someone walks on it. Wooden planks can be nailed together or may be cleated to provide further protection from slipping.
Very often wooden planks are utilized when versatility and changeability of the scaffold platform is required. For example, wooden planks are almost exclusively used in scaffolding of round tanks because the wooden planks can be arranged to follow the curvilinear path about the tank without creating a safety risk.
Wooden planks, however, also have certain disadvantages. For example wooden planks are very costly. The grading rules for wooden planks are more stringent than they are for any other structural use of wood. Hence the cost of wooden planks is very high since only the best grade of wood is utilized.
Another disadvantage of wooden planks is that they are susceptible to deterioration. This disadvantage is extremely significant due to the industrial environments in which wooden planks are used. For example, wooden planks may be exposed to acids, such as those used on buildings to clean stones and bricks. Other examples of the use of wooden planks in environments wherein careful monitoring is necessary include the use of wooden planks in or near oil refineries and paper mills, where corrosive chemicals specifically selected to break down wood fibers are present.
Because of safety concerns, each wooden plank must be inspected and tested before it can be used again. Ironically, repeated certification of wooden plank may, in fact, weaken it as a result of the testing procedure.
Attempts to overcome the disadvantages of wooden planks have resulted in the design of metal planks. While metal planks are not as expensive to maintain and are not as susceptible to deterioration as wooden planks, metal planks have not enjoyed success in the scaffold industry because of their own shortcomings. In particular, a slipping problem exists with metal planks because of insufficient friction between a metal plank and the metal scaffold frame, or metal scaffold plank, upon which it rests.
Attempts have been made to remedy the slipping problem associated with metal planks. These attempts have not met with much success. For example, one attempt to deal with this problem has been to place a plastic bead on the base of the metal plank. This plastic bead, however, is subject to abrasion during the erection of the scaffolding and does not bear impact well. Furthermore, adhesion of the bead is critical since an extremely dangerous situation would exist if the bead came away from the metal plank.
Another disadvantage of the metal plank arises from the design of this device which is most commonly used. Metal planks are generally fabricated by bending a metal sheet into a channel shape with short returns on the legs of the channel which add strength and provide the surface upon which the metal plank rests.
This design results in a space existing between the returns. When metal planks are lapped on top of each other, a risk exists that a return will slip off of a metal plank it is resting on, thereby resulting in the rotation of the upper metal plank about the lower metal plank and the creation of an unsafe condition. Metal strips have been used to close the space between the returns but these metal strips provide no slip resistance.